Conventionally, liquid hydrocarbons are produced to the surface of the earth from a subterranean hydrocarbon-bearing formation via a well penetrating and in fluid communication with the formation. Usually, a plurality of wells are drilled and placed in fluid communication with the subterranean hydrocarbon-bearing formation to effectively produce liquid hydrocarbons from a particular subterranean reservoir. Approximately 20 to 30 percent of the volume of hydrocarbons originally present within a given reservoir in a subterranean formation can be produced by the natural pressure of the formation, i.e. by primary production. Secondary recovery processes have been employed to produce additional quantities of original hydrocarbons in place in a subterranean formation. Such secondary recovery processes include non-thermal processes involving the injection of a drive fluid, such as water, via wells designated as injection wells into the formation to drive liquid hydrocarbons to separate wells designated for production of hydrocarbons to the surface. Successful secondary recovery processes may result in the recovery of about 30 to 50 percent of the original hydrocarbons in place in a subterranean formation. Once a secondary recovery process has been operated to its economic limit, i.e. the profit from the sale of hydrocarbons produced as a result of the process is less than the operating expense of the process per se, tertiary recovery processes have been utilized to recover an additional incremental amount of the original liquid hydrocarbons in place in a subterranean formation by altering the properties of liquid hydrocarbons, e.g. altering surface tension. Examples of tertiary recovery processes include micellar and surfactant flooding processes. Tertiary recovery processes also include processes which involve the injection of a thermal drive fluid, such as steam, or a gas, such as carbon dioxide, which is miscible with liquid hydrocarbons.
Secondary and tertiary recovery operations often involve the injection of a drive fluid via one or more wells designated as injection wells into the subterranean formation to drive liquid hydrocarbons in place to at least one or more separate wells designated as production wells for production of hydrocarbons to the surface. Another process commonly applied to a given well is a cyclic injection/production process. This process, also referred to as "huff-n-puff", entails injecting a fluid via the single well into a subterranean hydrocarbon-bearing formation so as to contact hydrocarbons in place in the near-wellbore environment of the subterranean formation surrounding the well. Thereafter, the well may be "shut in" for a period of time. The well is then returned to production and an incremental volume of liquid hydrocarbons is produced from the formation to the surface. Carbon dioxide, flue gas, and steam have been previously used in such cyclic injection/production process. Such cyclic injection/production processes as applied to a well involve a relatively small capital investment, and hence, a normally quick pay out period. However, a suitable source via pipeline or truck of carbon dioxide or nitrogen is often not available near the well to be treated. Moreover, the use of a thermal fluid, such as steam, requires relatively expensive surface equipment which may be impractical in remote or offshore locations due to constraints of space. Accordingly, a need exists for a cyclic injection/production process for the enhanced recovery of liquid hydrocarbons from a subterranean hydrocarbon-bearing formation through a well in fluid communication therewith which involves injection of a fluid which is readily and widely available and which can be implemented without large spatial requirements.
Thus, it is an object of the present invention to provide a process for the enhanced recovery of liquid hydrocarbons from a subterranean hydrocarbon-bearing formation which is easily implemented and operated.
It is another object of the present invention to provide such a process which utilizes a fluid which is normally available at a given well site and which results in the recovery of a significant increment of liquid hydrocarbons from the subterranean formation.
It is further object of the present invention to provide such a process which can be repeated in multiple cycles, each cycle resulting in the recovery of a significant increment of liquid hydrocarbon from the subterranean formation.
It is still a further object of the present invention to provide such a process which is relatively inexpensive.